1. Field of the Invention
The present invention relates to a process for bend-shaping a glass plate so that the glass plate has a complexly curved face and an apparatus for carrying out the process.
2. Discussion of the Background
In automobile industries, there has been an increasing demand for a glass plate having a complexly curved face, i.e. a glass plate 8 having a complexly curved face wherein a flat glass plate is bend-shaped with two different radius of curvatures R1 and R2 in its longitudinal and transversal directions as shown in FIG. 3.
FIG. 4 shows an example of a bend-shaping apparatus proposed as an apparatus for bend-shaping a glass plate to have a complexly curved face (Japanese Examined Patent Publication No. 10331/1974). With the use of a bend-shaping apparatus 10, a glass plate 8 is bend-shaped to have a radius R2 along the axis perpendicular to the transferring direction while it is transferred on hearth beds 13, 13 and then, the glass plate 8 is bend-shaped to have a radius R1 along the axis of the transferring direction on hearth beds 14, 16 each of which has a portion curved along the axis of the transferring direction, and then it is cooled and strengthened at a blowing port 18, whereby a complexly curved face is formed in the glass plate 8 as shown in FIG. 3.
A shaping furnace constitutes a very large portion of the investment for such glass manufacture line. Accordingly, it is advantageous if equipment for a conventional glass plate manufacture line for producing a glass plate having a simply curved face can be used for a glass plate manufacture line which is used for producing a glass plate having a complexly curved face. In particular, it is advantageous if the shaping furnace for the conventional manufacture line can be used in common. However, there were many difficulties in using the same shaping furnace for both types of curved glass plates. Namely, when it is desired that the glass plate manufacture line for a glass plate having a simply curved face, which is already equipped, is used for a glass plate manufacture line for a glass plate having a complexly curved face as shown in FIG. 4, it is necessary to replace the hearth beds 14, 16 and the blowing port 18 in the glass plate manufacture line for a glass plate having a simply curved face by those for a glass plate having a complexly curved face. In the conventional bend-shaping apparatus for producing a glass plate having a complexly curved face, however, there was a large distance in the vertical direction between the level H2 of the position where the glass plate is not yet bend-shaped and the level H1 of the position where the glass plate has been bend-shaped. The distance is indicated by H in FIG. 4. Namely, if the shaping furnace of the glass plate manufacture line for a glass plate having a simple curved face is to be used in common for the glass plate manufacture line for a glass plate having a complexly curved face, it is necessary to provide a special raising means for raising a glass plate, which has been bend-shaped in the longitudinal direction, from the lower level H1 to the higher level H2 in a case that the glass plate having a complexly curved face is to be manufactured.
The lower level H1 varies depending not only on the difference between the nature of the glass plate having a simply curved face and the nature of the glass plate having a complexly curved face but also on the specification of the glass plate having the complexly curved face. Namely, such raising means has to be either of an inclusive use which is separately prepared depending on the specification for bend-shaping the glass plate, or has to be used after the adjustment of an existing raising means depending on the specification. The preparation of several types of raising means for inclusive use depending on the type of glass plate is not preferable because a large investment for equipment is required. The adjustment of the existing raising means is not practical because much time and labor are required when the type of glass plate to be manufactured is changed. In addition, in practice, there are many difficulties from a technical viewpoint to raise the glass plate from the lower level H1 to the higher level H2.
Namely, in the conventional glass plate bend-shaping line for bend-shaping a glass plate having a simple curved face, the distance L between a shaping furnace 12 and a post-treating conveyor 20 is determined to be short (generally, several meters or less) in order to reduce equipment space as much as possible. Accordingly, when the shaping furnace in the existing glass plate shaping line for a glass plate having a simply curved face is used for the production of a glass plate having a complexly curved face, it is necessary to raise the glass plate from the lower level H1 to the higher level H2 in the relatively short distance L.
In such conditions, it is very difficult to stably transfer the glass plate in that distance because the radius of curvature and the gradient of the transferring surface of the blowing port 18 are different from those of the transferring surface of the raising means. Such difficulty can be eliminated if the distance L can be increased to more than 10 meters. However, this does not meet the demand of saving space, and it is impossible to use the existing manufacture line for a glass plate having a simple curved face for the manufacture line for a glass plate having a complexly curved face.
It is an object of the present invention to eliminate the disadvantage described above and to provide a process for bend-shaping a glass having a complexly curved face and an apparatus for carrying out the process, which enables the utilization of most of the equipment of the existing manufacture line for a glass plate having a simple curved face and which is sufficient for only simple change of equipment.
It is another object of the present invention to provide a process for bend-shaping a glass plate having a complexly curved face and an apparatus for carrying out the process which can operate in a small space of equipment.
Another object of the present invention is to permit the common use of the shaping furnace for a glass plate having a simply curved face and the shaping furnace for a glass plate having a complexly curved face in spite of various kinds of specification.
Another object of the present invention is to standardize an amount of a decrease in elevation of a glass plate from a higher position H2 (the position of the glass plate before falling) to a lower position H1 (the position after the falling) during the operation of shaping the glass plate to have a complexly curved face, so that a raising means to raise the glass plate can be used commonly irrespective of the specification of bending the glass plate having a complexly curved face. Thus labor necessary for adjusting the equipment for bend-shaping the glass plate at the time of changing the specification of the glass plate can be reduced.
It is another object of the present invention to improve stability in raising the bent glass plate by reducing the length of transferring the glass plate.
In accordance with the present invention, there is provided a process for bend-shaping a glass plate by heating the glass plate to a temperature which is close to a softening temperature of the glass plate, while the glass plate is transferred in a transferring direction along a transferring surface in a shaping furnace, to thereby bend the glass plate, by its own deadweight, into a shape corresponding to the shape of the transferring surface, comprising the steps of:
complexly bending the glass plate in the shaping furnace by transferring the glass plate along a complexly bending transferring surface comprising hearth beds having bend-shaping surfaces, said complexly bending transferring surface having a complexly curved face which is upwardly projected with predetermined radius of curvatures along both an axis of the transferring direction and an axis perpendicular to the transferring direction, said transferring surface being formed of a continuous surface having substantially the same radius of curvatures as the surface of the glass plate to be formed, and said transferring surface having an upward gradient portion at at least an area near an exit of the shaping furnace, whereby the glass plate is bent into a shape which substantially corresponds to that of the complexly bending transferring surface;
transferring the glass plate through the shaping furnace by utilizing a driving chain having holders for holding the glass plate in a floating state and a pusher for pushing the held glass plate when the driving chain is driven in the transferring direction; and
cooling and strengthening the glass plate by transferring the glass plate, which has been delivered through the exit of the shaping furnace, along a cooling transferring surface which has a complexly curved face so as to be substantially continuous to that of the complexly bending transferring surface and which has a downward gradient portion in at least a part of the cooling transferring surface wherein the glass plate is held in the floating state by a gas layer formed of gas which is blown from the lower part of the complexly bending transferring surface when the glass plate is transferred along the complexly bending transferring surface.
Further, the process for bend-shaping a glass plate of the present invention may have a moving step of moving the glass plate to the level of a post-treating transferring path after the cooling and transferring step.
Further, the process for bend-shaping a glass plate according to the present invention comprises, before the complexly bending step, a simple bending step of transferring the glass plate in a substantially horizontal direction along a simple bending transferring surface having a simple curved face which is upwardly projected with predetermined radius of curvatures along the axis perpendicular to the transferring direction in the shaping furnace, whereby the glass plate is bent into a shape which substantially corresponds to that of the simple bending transferring surface.
Further, in accordance with the present invention, there is a step of transferring in a floating state the glass plate by means of a transferring surface in the shaping furnace before the complexly bending, said transferring surface being detachable and replaceable so that gradient in the transferring direction is gradually changed to have a predetermined gradient depending on an upward gradient of the complex bending transferring surface.
Further, in accordance with the present invention, there is provided an apparatus for bend-shaping a glass plate wherein the glass plate is heated to a temperature which is close to a softening temperature of the glass while the glass plate is transferred in a transferring direction along a transferring surface in a shaping furnace, to thereby bend by its deadweight the glass plate into a shape corresponding substantially to that of the transferring surface which comprises:
a shaping furnace for heating the glass plate to a temperature which is close to a softening temperature of the glass plate,
a complexly bending transferring surface positioned in the shaping furnace, which has a complexly curved face so as to upwardly project along both an axis of the transferring direction and an axis perpendicular to the transferring direction and which has an upward gradient portion at at least an area near an exit of the shaping furnace, said transferring surface being formed of a continuous surface having substantially the same radius of curvatures as the surface of the glass plate to be formed, and
a cooling transferring surface which has a complexly curved face so as to be substantially continuous to that of the complexly bending transferring surface and which has a downward gradient portion in at least a part of the cooling transferring surface; and
a glass plate cooling and strengthening means disposed near the cooling transferring surface wherein the complexly bending transferring surface is provided by hearth beds in the shaping furnace, said hearth beds defining bend-shaping surfaces; and
the complexly bending transferring surface is provided with a holding means which ejects gas from the lower part of the complexly bending transferring surface to hold and transfer the glass in a floating state by a gas layer formed of gas, the holding means further comprising a driving chain which is movable in the transferring direction, the driving chain comprising holders for holding the glass sheet in the floating state and a pusher for pushing the held glass sheet when the driving chain is driven.
Further, the apparatus for bend-shaping a glass plate of the present invention may have a moving means to move the glass plate to the level of a post-treating transferring path, which is positioned at the downstream side in the transferring direction of the cooling transferring surface.
Further, the apparatus for bend-shaping a glass plate of the present invention may have a simple bending transferring surface which is positioned at the upstream side in the transferring direction of the complexly bending transferring surface and which has an upwardly projecting simple curved face along the axis perpendicular to the transferring direction.
Further, in accordance with the apparatus for bend-shaping a glass plate of the present invention, there is a transferring surface provided at an upstream side in a transferring direction of said complexly bending transferring surface, said transferring surface being detachable and replaceable so that gradient in the transferring direction is gradually changed to have a predetermined gradient depending on the upward gradient of the complexly bending transferring surface.
In accordance with the technique described above, the glass plate transferred along the transferring surface located in the shaping furnace is heated to the nearly glass softening temperature in the shaping furnace so that it is shaped by its deadweight to have a complexly curved face which corresponds to the shape of the transferring surface; the glass plate is cooled and strengthened by means of the cooling and strengthening means; and then, it is introduced in the post-treating transferring path which transfers the glass plate to a place where a post-treatment such as washing is carried out.
In such a technique, any type of shaping furnace for bend-shaping a glass plate may be used as far as the shaping furnace includes a heating means for heating the glass plate as an object to be shaped to the temperature of softening and a transferring surface for transferring thereon the glass plate. In this case, the heating means may be of a type using a radiation heat by a heater.
Further, the heating means may be of such a type that a hot gas is ejected from the lower part of the hearth beds which are normally constituted by refractory bricks, through apertures formed in the hearth beds so that the glass plate is heated to nearly the glass softening temperature. In the later case, the glass plate is held in a floating state by a layer formed of the gas. This means that the hearth beds of the shaping furnace constitute the above-mentioned transferring surface. The discharging of the hot gas from the lower part of the hearth beds eliminates the contact of the glass plate to the transferring surface, and accordingly, a flaw on the glass plate is prevented from occurring during the transfer. This is a preferable embodiment from the viewpoint of preventing a flaw on the glass plate.
The design of the glass plate cooling and strengthening means may be changed as desired as far as the glass plate can be strengthened in the shaping furnace while the shape of the shaped glass plate can be kept. It is in particular preferable to use the glass plate cooling and strengthening means having such a construction that a cooling air blowing port module group wherein a number of nozzle-like blowing ports are arranged with appropriate intervals above and below the transferring path for transferring the glass plate, are provided whereby the glass plate is cooled and strengthened from the upper and lower parts by air ejected from the blowing ports. Such construction is desirable from the viewpoint of uniformly strengthening the glass plate. Further, it is possible to carry out cooling operation in two stages: the primary cooling wherein the glass plate is cooled to a temperature lower than the distortion point while it is uniformly strengthened, and the secondary cooling wherein the glass plate is cooled to the substantially room temperature. The investment needed for the cooling blowing port module can be saved if the module group is used for only the primary cooling.
As means for transferring the glass plate in the present invention, there is the complexly bending transferring surface positioned in the shaping furnace, which has a complexly curved face so as to upwardly project along both the axis of the transferring direction and the axis perpendicular to the transferring direction and which has an upward gradient portion at at least an area near the exit of the shaping furnace, and the cooling transferring surface which has a complexly curved face so as to be substantially continuous to that of the complexly bending transferring surface and which has a downward gradient portion in at least a part of it.
The complexly bending transferring surface is formed of a continuous surface which has substantially the same radius of curvatures as the surface of the glass plate to be shaped. Namely, it has a complexly bending surface which is different from a transferring surface in a waveform which is provided by, for instance, an arrangement of rollers, but it has a continuous smooth surface provided by a single hearth bed. Alternatively, there may be a complexly bending transferring surface positioned in the shaping furnace, which has a complexly curved face so as to downwardly project along both the axis of the transferring direction and the axis perpendicular to the transferring direction and which has a downward gradient portion at at least an area near the exit of the shaping furnace, and a cooling transferring surface which has a complexly curved face so as to be substantially continuous to that of the complexly bending transferring surface and which has an upward gradient portion in at least a part of it. The difference of the transferring surfaces between the former case and the later case is only the direction of the projection of the curved surfaces, and they can be considered to be substantially the same. Accordingly, description will be provided as to the former case, namely, the case of forming a glass plate having a complexly curved face which projects upwardly.
The inclination angle of the upward gradient can be determined depending on the shape of a glass plate to be shaped. The radius of curvature of the transferring surface is also determined so as to correspond to a shape with which the glass plate is shaped. In the present invention, it is preferable that the radius of curvature along the axis perpendicular to the transferring direction is 500 mm or longer, more preferably, 1,000 mm or longer, and the radius of curvature along the axis of the transferring direction is 10,000 mm or longer, more preferably, 20,000 mm or longer.
The radius of curvature of the transferring surface can be optionally determined depending on a position on the transferring surface. For instance, the radius of curvature can be large at the initial stage of transferring and is gradually decreased toward the downstream side of the transferring path, whereby the glass plate has a shape substantially corresponding to a predetermined shape of bend in the area near the exit of the shaping furnace.
In the present invention, glass plates having various shapes of a complexly curved face can be produced depending on the needs in manufacturing. In this case, it is preferable to add a moving means at the downstream side in the transferring direction of the cooling transferring surface to thereby move the glass plate to the level or the height of the post-treating transferring path, from the standpoint that an existing manufacture line for glass plates having a simply curved face can be easily applied to manufacture glass plates having a complexly curved face. With the moving means, it is possible to transfer the glass plates to the post-treating transferring path by simply adjusting an angle of inclination of the moving means wherein the post-treating step is unchanged, whereby various kinds of glass plate having different kinds of radius of curvature can be easily produced. Any type of moving means, i.e. a disk conveyor, a belt conveyor or the like can be utilized as far as it can move the glass plate.
It is effective to provide a transferring surface having a predetermined gradient which is changeable as desired, at an upstream side in the transferring direction of the complexly bending transferring surface. The transferring surface is adapted to change the gradient depending on a shape of the glass plate to be formed to have a complexly bent surface. For instance, when the complexly bending transferring surface have a relatively large upward gradient portion, the transferring surface formed to have a certain upward gradient is disposed at the upstream side of the complexly bending transferring surface. On the other hand, when the upward gradient portion of the complexly bending transferring surface is not so large, the transferring surface capable of transferring the glass plate horizontally until the complexly bending step is conducted, is provided. Namely, the transferring surface disposed at the upstream side of the complexly bending transferring surface is so adapted that the upward gradient can be gradually increased so as to correspond to a large upward gradient of the complexly bending transferring surface.
In a case where it is necessary to bend-shape a glass plate deeper along only one direction as a windshield glass for automobile (one direction means the horizontal direction when the windshield glass is attached to an automobile), it is preferable to provide a simple bending transferring surface at the upstream side of the complexly bending transferring surface, wherein the simple bending transferring surface has a predetermined radius of curvature which curves along only the axis perpendicular to the transferring direction. In this case, a bending operation may be applied to a glass plate along the axis perpendicular to the transferring direction, before forming a complexly bending face, by transferring the glass plate on the simple bending transferring surface in the shaping furnace so that the direction of bending the glass plate to have a smaller radius of curvature coincides with the direction perpendicular to the transferring direction.
Further, in the above-mentioned case, if there is a difference in inclination near the boundary between the complexly bending transferring surface and the simple bending transferring surface, a glass plate may contact with the complexly bending transferring surface when the glass plate passes the boundary region, so that a strain or a defect may take place in the glass plate. In the present invention, however, occurrence of such a strain or defect can be prevented since a transferring surface inclined to have a slightly upward gradient portion in the transferring direction, i.e., the simple bending transferring surface in this specified case, is disposed at the upstream side of the complexly bending transferring surface so as to be inclined so that the simple bending transferring surface is slightly inclined upwardly in the transferring direction. When there is a difference in inclination between the simple bending transferring surface and the complexly bending transferring surface, the glass plate may be reversely bent at the boundary region. However, this causes no problem because the glass plate is shaped in the final shape above the complexly bending transferring surface after it has been passed through the boundary region.